Conventionally, hydrogenated fats such as hardened fish oil and vegetable oil have been used as raw materials for plastic fats because such a fat can provide good physical properties and functions. However, in recent years, the use of the hydrogenated fats has been limited because the hydrogenated fats contain trans-fatty acids that cause human heart diseases, and thus the replacement of the hydrogenated fats with palm oil and the like is recommended.
It is known that the combination of the palm oil as a main material in the plastic fat such as margarine and shortening is apt to cause changes such as the formation of coarse crystals and the increase in hardness during storage or distribution, and also, is not able to provide a plastic fat that can highly contain air. Hence, a triglyceride structure in the palm oil has been modified by transesterification.
For example, Patent Document 1 discloses a fat composition that can suppress quality change over time by mixing palm oil or palm stearin and a fat containing lauric acid in a certain fatty acid ratio and transesterifying the mixture. Furthermore, Patent Document 2 discloses a fat composition capable of producing a plastic fat that can eliminate the formation of coarse crystals and lead to a few changes over time by transesterifying a liquid vegetable oil containing a palm-based fat and unsaturated fatty acids in large amounts to make a component ratio of dipalmitoyl monooleoyl glyceride PPO/POP≧0.5 (P: palmitic acid, O: oleic acid). These modifying methods change the triglyceride POP in the palm oil into other components and achieve a certain effect on the suppression of the changes over time, but the effect is insufficient. These methods have another problem. For example, the methods simultaneously form tri-saturated triglycerides having a high melting point to reduce solubility in a mouth.
There are also disclosed methods for improving qualities of a plastic fat and chocolate that contain palm oil by using a fat composition that specifies the type or bonding site of a fatty acid constituting triglycerides. For example, Patent Document 3 discloses a fat composition that can prominently increase the crystallization rate by incorporating an XXM type triglyceride (X: a C>15 saturated chain, M: a C<15 saturated chain) in a small amount into a fat that has a low crystallization rate and is a low trans-fatty acid, such as the palm oil. Patent Document 4 discloses that a 1,3-di(S)-2-mono(X) type triglyceride (SXS) bonded with a saturated fatty acid (X) having 12 or less carbon atoms at the 2-position and bonded with saturated fatty acids (S) each having 16 or more carbon atoms at the 1- and 3 positions can suppress bloom of chocolate. These methods are effective on the suppression of coarse crystal formation in a plastic fat and the suppression of the bloom of chocolate, but have small suppressive effect on the changes over time.
In recent years, a low-calorie fat has been drawing attention as a health functional fat, and there are disclosed some triglycerides containing, in a molecule, a saturated long chain fatty acid having 16 or more carbon atoms and a medium chain fatty acid having 10 or less carbon atoms (for example, Patent Document 5 and Patent Document 6).
Furthermore, Patent Document 7 discloses an intermolecular compound of (a) a di-saturated medium chain fatty acid mono-long chain fatty acid triglyceride and (b) a 1,3-disaturated long chain fatty acid 2-monounsaturated long chain fatty acid triglyceride, and the intermolecular compound has a longer interplanar spacing of 65 {acute over (Å)} or more as determined by X-ray diffraction. It is described that the intermolecular compound can maintain a smooth texture of chocolate containing cacao butter in a large amount and can suppress the formation of bloom. Moreover, it is described that the intermolecular compound is also effective for the suppression of the hardness change of a plastic fat over time. The literature discloses no specific method for use of the plastic fat. However, it is not easy to obtain a composition that contains the di-saturated medium chain fatty acid mono-long chain fatty acid triglyceride at a high concentration, which can provide the intermolecular compound having a longer interplanar spacing of 65 {acute over (Å)} or more as determined by X-ray diffraction. Moreover, the presence of the di-saturated medium chain fatty acid mono-long chain fatty acid triglyceride in an equimolar amount to that of the 1,3-disaturated long chain fatty acid 2-monounsaturated long chain fatty acid triglyceride softens the plastic fat too much or lead to a lower melting point. Therefore, it is not preferred to use the intermolecular compound for margarine and shortening as a main material.